U.S. patent number 3,869,665 [Application Number 05/413,973] was granted by the patent office on 1975-03-04 for device for detecting corona discharge in an enclosed electric device.
This patent grant is currently assigned to Tokyo Electric Power Co., Ltd., Tokyo Shibaura Co., Ltd.. Invention is credited to Hiroshi Kenmochi, Shinichi Menju, Kunio Takahashi.
United States Patent |
3,869,665 |
Kenmochi , et al. |
March 4, 1975 |
DEVICE FOR DETECTING CORONA DISCHARGE IN AN ENCLOSED ELECTRIC
DEVICE
Abstract
In an enclosed electric device in which a conductor to be
charged with a voltage is supported by an insulation support in its
enclosing metal case, an electrode is disposed on or in the
insulation support so as to provide a first static capacitance with
respect to the conductor and a second static capacitance with
respect to the metal case. A corona discharge detector is connected
between the electrode and the metal case and adapted to detect,
with the first static capacitance used as a coupling capacitor, a
corona discharge occurring from the conductor and the insulation
support.
Inventors: |
Kenmochi; Hiroshi (Fujisawa,
JA), Menju; Shinichi (Atsugi, JA),
Takahashi; Kunio (Yokohama, JA) |
Assignee: |
Tokyo Shibaura Co., Ltd.
(Kawasaki-shi, JA)
Tokyo Electric Power Co., Ltd. (Tokyo, JA)
|
Family
ID: |
14591801 |
Appl.
No.: |
05/413,973 |
Filed: |
November 8, 1973 |
Foreign Application Priority Data
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|
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Nov 10, 1972 [JA] |
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47-112641 |
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Current U.S.
Class: |
324/72; 174/11R;
324/133; 324/536 |
Current CPC
Class: |
H02B
13/065 (20130101); G01R 27/18 (20130101); H02G
5/068 (20130101) |
Current International
Class: |
G01R
27/16 (20060101); H02B 13/035 (20060101); G01R
27/18 (20060101); H02B 13/065 (20060101); G01r
031/02 (); G01r 031/12 () |
Field of
Search: |
;324/72,54,126,133 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Smith; Alfred E.
Assistant Examiner: Hille; Rolf
Attorney, Agent or Firm: Flynn & Frishauf
Claims
1. In an enclosed electric device in which a conductor to be
charged with a voltage is supported within an enclosing metal case
by a plurality of insulation supports spaced apart from each other
along said conductor, said enclosing metal case being filled with
an insulating gas,
a corona discharge detecting device comprising:
a plurality of electrodes each coupled to a respective insulation
support for providing a first static capacitance (C1) relative to
said conductor and a second static capacitance (C2) relative to
said enclosing metal case; and
a corona discharge detector adapted to be connected in parallel
with said second static capacitance (C2) and to detect, with said
first static capacitance (C1) serving as a coupling capacitor, a
corona discharge
2. A corona discharge detecting device according to claim 1
wherein:
said metal case includes a plurality of serially connected unit
metal cases;
each of said insulation supports is sandwiched in an airtight
manner between adjacent unit metal cases at the outer side thereof
opposite to the inner side on which said conductor is
supported;
said electrodes are provided on the outer exposed surface of said
outer side of said respective insulation supports; and
said corona discharge detector is adapted to be connected between
said
3. A corona discharge detecting device according to claim 1
wherein:
said metal case includes a plurality of serially connected unit
metal cases;
each of said insulation supports is sandwiched in an airtight
manner between adjacent unit metal cases at the outer side thereof
opposite to the inner side on which said conductor is
supported;
said electrodes are embedded near said sandwiched portion and said
respective insulation supports, and have respective outer
connection conductors taken out therefrom; and
said corona discharge detector is adapted to be connected between
said outer connection conductors and said metal case.
Description
This invention relates to a corona discharge detecting device, and
particularly to a corona discharge detecting device capable of
detecting a corona discharge, and its location, occurring on an
electric device enclosed within a metal case.
A high tension enclosed electric device is enclosed by supporting
its conductor to be charged with a voltage by one end of an
insulation support and securing the other end of the insulation
support to its enclosing metal case. With an enclosed interrupter
of a very high voltage and of a high rated capacity, for example, a
very long bus bar is used, and to enclose the bus bar, a plurality
of unit bus bars and unit metal cases are often serially assembled
on the spot. After the assembly is completed, an insulation gas
such as sulfur hexafluoride SF.sub.6 is sealed into the metal case
assembled serially. The SF.sub.6 gas exhibits a better insulation
characteristic under a uniform electric field than the other
gaseous insulation medium. However, its insulation characteristic
is markedly deteriorated under a non-uniform electric field. The
disturbance of electric field with the enclosed metal case after
assembly is influenced by an assembly technique on the spot, a
penetration of water through the serially connected portion of
adjacent unit metal cases, or presence of dust, grease, metal
particles etc. deposited on the surface of the insulation support
during assembly. Even if each unit is satisfactory in a factory
test, a corona discharge often occurs, after assembly, on a charged
portion, particularly a conductor portion supported by the
insulation support, or a flashover takes place on the surface of
the insulation support. As a means for detecting such a corona
discharge, the customary practice is to apply an AC voltage from a
power source through an impedance to between the metal case and the
conductor; connect a series circuit, consisting of a coupling
capacitor and a detection impedance, in parallel with a static
capacitance created between the metal case and the conductor; and
measure a voltage across the detection impedance using a corona
detector, for example, a corona meter. According to this method, it
is necessary that the coupling capacitor be prepared on the spot
and that one end of the coupling capacitor be connected directly to
the conductor. However, it is only possible to connect one end of
the coupling capacitor to one end of a lengthy bus bar which
extends through a bushing. Even if detection is made according to
such method difficulty is encountered in detecting a location at
which a corona discharge occurs. It is also known to acoustically
detect a corona discharge using an electrical acoustic converter.
However, it is very difficult to detect a corona discharge, and its
location, due to poor sensitivity of the converter.
It is accordingly the object of this invention to provide a corona
discharge detecting device for an enclosed electric device, capable
of easily detecting a corona discharge and its location without the
necessity of any particular outer coupling capacitor.
SUMMARY OF THE INVENTION
In an enclosed electric device in which a conductor to be charged
with a voltage is supported by an insulation support in its
enclosing metal case, a corona discharge detecting device according
to this invention comprises an electrode disposed on or in the
insulation support so as to provide a first static capacitance
relative to the conductor and a second static capacitance relative
to the metal case, and a corona discharge detector connected in
parallel with the second static capacitance and adapted to detect,
with the first static capacitance used as a coupling capacitor, a
corona discharge occurring from the conductor and the insulation
support.
One end of the insulation may be sandwiched in an airtight manner
between the serially connected ends of adjacent unit metal cases
and the electrode may be mounted on the outer exposed surface of
sandwiched end of the insulation support. An electrode may be
embedded in the insulation support at the position near the
sandwiched portion. In this case, a conductor is taken out from the
electrode for outward connection. In either case, a corona
discharge detector is connected between the electrode and the metal
case. The electrode can be mounted on said outer exposed surface of
said sandwiched portion of the insulation support, only when a
corona discharge is measured.
According to this invention, it is not required that a coupling
capacitor be prepared on the spot. Furthermore, it is possible to
locate a place at which a corona discharge takes place.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows one embodiment according to this invention capable of
detecting a corona discharge occurring at the insulation support
for a bus bar of an enclosed high tension interrupter;
FIG. 2 is an enlarged cross-sectional view taken along line II--II
of FIG. 1;
FIG. 3 is a cross-sectional view taken along line III--III of FIG.
2;
FIG. 4 is an enlarged view of a modification according to this
invention taken along line IV--IV of FIG. 1; and
FIG. 5 is a cross-sectional view taken along line V--V of FIG.
4.
DETAILED DESCRIPTION OF ILLUSTRATED EMBODIMENTS
In FIGS. 1 to 3, a conductor or a bus bar 10, for example, to be
charged with a voltage and a metal case 11 for enclosing the bus
bar 10 are extended in the direction of x to be connected to an
enclosed electric device (not shown), for example, a high tension
interrupter. The metal case 11 includes a plurality of unit metal
cases 11a serially coupled together by means of bolts 14 with the
outer peripheral end of an insulation support 13 sandwiched between
respective end flanges 12 of the adjacent unit metal cases. Near
the inner peripheral end of the insulation support 13, the outer
peripheral end of a circular metal ring 15 (FIG. 3) is embedded. On
the substantially center of a connecting member 16 a flange 17 is
secured by welding etc. The flange 17 is secured by bolts 18 to the
metal ring 15. The bus bar 10 is also sectionalized into unit bus
bars 10a. As shown in FIG. 3 the unit bus bars are serially
connected together by inserting one end of the connecting member 16
into the opening end of one unit bus bar and the other end of the
connecting member into the opening end of the other unit bus bar,
and are supported by the insulation support member 13. Along the
outer periphery of the insulation support sandwiched by the flanges
12 an electrode 19, for example, a metal tape, is provided. The
unit metal case 11a is grounded. In the above-mentioned arrangement
a first static capacitance C1 is formed between the electrode 19
and the bus bar 10 and a second static capacitance C2 is formed
between the electrode 19 and the metal case.
After the assembly of the enclosed interrupter is completed as
shown in FIG. 1, an insulation gas, for example, sulfur
hexafluoride SF.sub.6 is filled in the closed case. Where corona
discharge is measured, a corona discharge detector 20 comprising a
detection impedance ZD and a measuring section M which are in
parallel connection is connected between the electrode 19 and the
metal case (ground potential) at a serial junction portion of two
unit cases 11a. Between the metal case and the bus bar portion
derived from a bushing 21 (FIG. 1) a high voltage from a secondary
winding of a transformer 22 is applied. Suppose that a corona
discharge occurs either on the bus bar portion supported by the
insulation support 13 or on the insulation support member. As a
corona discharge current is a pulse current very short in its
duration and contains frequency components over a wide range of
below several M Hz. It is therefore preferred that detection be
made by extracting the frequency component present in a specified
frequency band. Explanation is now made of one example of the
corona discharge detector 20 as shown in FIG. 1. The intermediate
frequency component, for example, 500 kHz of a corona current is
taken out from a secondary circuit tuning type transformer coupling
detection circuit 24 (corresponding to the detection impedance ZD
as shown in FIG. 3), and an output is attenuated to a proper extent
by an attenuator 25 and amplified by a tuning amplifier 26. The
output of the amplifier is detected through a detection circuit 27
and shaped by a pulse shaping circuit 28, and said corona discharge
is detected by an indicator 29 such as a potentiometer,
oscilloscope etc.
As is evident from FIG. 3 the first static capacitance C1 serves as
a coupling capacitance to a corona detector 20. When a corona
discharge occurs at the insulation support member 13, a corona
current is flowed through the detection impedance ZD through the
coupling capacitance C1 (about 0.05 pF), and the generation of a
corona discharge can be detected.
Even if the corona detector 20 is connected to an electrode at the
insulation support located in a position other than that shown in
FIG. 3, when a corona discharge does not occur at this location,
then a corona discharge as occurring at the insulation support as
shown in FIG. 3 can not be detected due to a low sensitivity of the
corona detector. In other words, the location at which a corona
discharge occurs can be positively located.
There will be explained by reference to FIGS. 4 and 5 another
embodiment according to this invention in which like reference
numerals as used in the embodiment shown in FIGS. 2 and 3 are
employed to denote like parts or elements. With this embodiment, a
ring-like electrode 30 is embedded in and near the outer periphery
of an insulation supporting body 13 sandwiched between flanges 12,
and an outer connection conductor 31 is taken out from this
electrode. The conductor 31 is normally connected to a unit metal
case 11a and used also to correct a non-uniform electric field
distribution within a metal case. When a corona discharge is
detected, the conductor 31 is taken out, as shown in FIG. 5, from
the metal case and connected to a corona discharge detector 20. The
provision of a first static capacitance C1 and a second static
capacitance C2 as well as the operation and effect of a corona
discharge detecting device is substantially the same as the
embodiment shown in FIGS. 1 to 3 and further explanation is
omitted.
The kind of the enclosed electric device and the shape of the
enclosing metal case should not be taken in a limiting way, as long
as they do not depart from the spirit and scope of this invention.
Farther, the insulation gas filled into the metal receptacle is not
limited to the SF.sub.6 gas.
* * * * *